Eric Sugarman should probably know better. But hey, sometimes you just can't help yourself.

So even though the Vikings head athletic trainer spent the past five months preaching the need to keep Adrian Peterson's superhuman ambition from becoming dangerous, occasionally he likes to press a button or two.

You know, just to check if Peterson's relentless positivity can be tested.

That's why, in the corner of the Vikings training room, a few paces from the in-pool treadmill Peterson used during the early stages of his knee rehabilitation, Sugarman took the liberty of doctoring the art.

The new version? Sugarman changed the expression, cutting the running back's head from a photo taken last Christmas Eve and taping it to the canvas. That picture, snapped moments after Peterson blew out his anterior cruciate and medial collateral ligaments at Washington, captures the Vikings star with an agonizing grimace.

"Everybody's got jokes. Ha ha. It's funny. But I'm seriously getting ready to rip that picture off. When I see it, it's always a big reminder of that day. And I'm kind of tired of looking at it. I need to find me a razor blade and go to work."

Maybe this is part of the reason Peterson has attached himself so firmly to his own projected full-recovery date.

The faster Peterson heals, the sooner he can bury that painful memory from last winter.

Testing positive

So put an "X" through Dec. 24, 2011.

Peterson is locked in on another date: Sept. 9, 2012.

That's the day the Vikings open the regular season against Jacksonville. That's now 14 weeks away.

"What I envision is to be suited up and ready to roll. Full strength," Peterson said. "Anything else? I would be cheating myself."

Still, before fast-forwarding, perhaps it's appropriate to rewind first to the New Year's Eve Peterson never wanted to experience. That night is commemorated through pictures he tweeted from a hospital bed in Birmingham, Ala., just a day after Dr. James Andrews sliced into his left knee to repair his severely damaged ACL and MCL.

In those photos, Peterson wears a playful smirk and a plastic "HAPPY NEW YEAR" derby. He has a noisemaker hanging from his lips and a pint of Blue Bell vanilla ice cream in his hand.

Hey, if he was going to be confined to a hospital bed as 2011 turned into 2012, why not at least deliver a good-humored spin move?

"I was feeling a little loopy," Peterson confessed. "I wanted to have a good time too and show everyone I was in good spirits and planning to handle this the best way possible. I wasn't going to sit around and sulk."

As daunting as the rehab process seemed, Peterson immediately vowed to use positive energy as his secret weapon.

"Attitude is critical with this," said Russ Paine, the physical therapist Peterson is working closely with in Houston. "If you're not really stable with who you are, an injury like this can be a huge blow to your ego. You're the king of the hill, then all of a sudden -- uh-oh.

"But Adrian? He's been energetic since the day I met him."

That's not to say there wasn't any depression. Sugarman notes that during the two weeks after surgery, Peterson's pain was intense. Moving around in slow-motion, Peterson said, proved frustrating.

The sleep deprivation made him angry.

"You think he's Adrian Peterson. Invincible. Doesn't bleed when you cut him," Sugarman said. "But for those two weeks? He was a disaster. Every morning, coming in and laying on that [trainer's] table and he was about as miserable as a human being could be. He was calling me late at night, texting me with hate messages.

"He didn't shave. He lost weight. He hurt. And I took the brunt of it."

For two weeks and two weeks only. After that, self-pity might as well have been a slow-footed, 160-pound defensive back trying to corral Peterson in the open field.

Out of the ordinary

In Houston, Peterson's drive has been on full display.

Paine, one of Andrews' endorsed therapists, has a handful of NFL players he's helping rehab injuries this offseason. That group includes Packers cornerback Tramon Williams, Buccaneers defensive tackle Amobi Okoye and free-agent safety James Ihedigbo.

"Even they recognize Adrian's different," Paine said. "He has a different protoplasm than the rest of the world."

Peterson will tell anyone who listens that immediately after his surgery, doctors told him it would take three days to regain enough strength to lift his leg. Yet as that warning was being issued, Peterson was already elevating his leg.

Last month, while guiding Peterson through a balance session at Winter Park, Sugarman called for a water break. Ten minutes later, he couldn't find Peterson. Turns out the running back had bolted to pump out a few reps on the leg press.

That's been the biggest challenge for those overseeing Peterson's recovery: making sure his drive doesn't become self-destructive.

Paine faced a similar challenge in 2000 when, as an assistant team physician to the Houston Rockets, he was helping Charles Barkley work back from a torn quadriceps tendon. Barkley was always trying to accelerate the customary patient timeline.

"I'd tell him, 'Charles, you've got to do these things by the standard. I know you think you're special. But your quad tendon doesn't know it's in Charles Barkley's body,' " Paine said. "And he looked at me with a smile and said, 'Oh, yes it does.' "

Peterson is similarly wired. Darn proud of it, too.

"With the experts, I'm sure 90 or 95 percent of the time, they're right with their estimates," he said. "But there are some guys you can't put the traditional timetable on. Some guys are different. I just happen to feel I'm one of those guys."

One-track mind

At this stage, Peterson has done two Winter Park rehab workouts in front of the media. The most recent came Wednesday.

He shuffled while chasing a soccer ball in a sand pit.

He ran sprints with receiver Percy Harvin, sprinting up a steep hill beside the practice field each time.

Peterson also ran full speed in the end zone as Sugarman restricted his progress with a parachute apparatus, then suddenly released him to run free.

"I was having a heck of a time holding him back," Sugarman said.

That's been the challenge all along.

Plus, it's only going to get harder as Peterson continues to see Vikings teammates practicing and working toward that season opener.

For now, he remains ahead of schedule. His full range of motion has returned. He looks great and feels better.

But Paine issues a reminder of the phases Peterson has yet to clear. His left quadriceps still needs strengthening. Then there's the inescapable need to regain proprioception -- getting his knee to reach a state of equilibrium and balance with the rest of his body. That takes time.

So while Sugarman supports Peterson's urge to be ready for Week 1, he isn't crazy enough to promise it.

"In reality, he is only going to be back on the field when he is functionally safe to go on the field. Not just because he wants to say, 'Oh, I did it. I'm the greatest.' There's a lot more to it."

Which leads to the one question that seems to confound Peterson: What happens if Sept. 9 arrives and he is not ready to play?

"I don't know how to answer that question," Peterson said. "And I struggle to even entertain it. Because that's not the way my mind is tuned in. I can't let that negativity seep in. My mindset is that I will be there. I want to be playing. Forget what everyone else says."

OK.

So Sept. 9 remains the goal until it's no longer possible. Then, if need be, Peterson will readjust.

"No," Peterson asserted. "The goal is the goal. And I'm going to accomplish it."